Drafting instruments such as compasses, protractors, rulers and T-squares are well known. However, the combination of these tools has been fairly limited. Specifically, there is no drafting tool currently available that combines the protractor, T-square, compass and ruler functions in one easy-to-use tool fabricated from as little as two parts. The prior art only taught complicated, multi-component instruments that are expensive to manufacture and difficult to use. Further, there is no currently available drafting tool that combines the protractor, T-square, compass and ruler functions that is also suitable for use on dry erase boards.
Limited combinations of various drafting tools are shown in the prior art. For example, U.S. Pat. No. 3,378,927 discloses a drafting implement which can draw parallel lines on the blackboard and strike arcs about a center located near the edge of a blackboard. However, the device disclosed cannot draw circles, function as a protractor, or mark off distances. Further, the device of U.S. Pat. No. 3,378,927 is fabricated from at least ten different parts.
By contrast, U.S. Pat. No. 1,447,207 discloses a device that can function as a compass to draw a circle, as a protractor and further as a ruler, but the device has no capacity to function as a T-square or draw parallel lines. Despite its limited use, the device shown in U.S. Pat. No. 1,447,207 is fabricated from three separate parts.
U.S. Pat. No. 2,104,515 discloses a T-square for use on blackboards that also includes a protractor of limited value. The device disclosed in U.S. Pat. No. 2,104,515 also includes a complicated means for attaching the device to the blackboard which interferes with its use as a ruler but is fabricated from eight or more separate parts. U.S Pat. No 2,581,839 also discloses a drawing instrument for use on a blackboard. The device operates as a protractor, ruler and compass but not as a T-square. Further, the device shown in U.S. Pat. No. 2,581,839 includes multiple parts (approximately six parts) and therefore is expensive to manufacture.
Thus, there is a need for a simple, yet effective, inexpensive drafting instrument that combines the functions of a protractor, T-square, ruler and compass in one simple, easy-to-use instrument. Further, there is also a need for a drafting instrument for use on dry erase boards and on chalkboards that combines the compass, protractor, T-square and ruler functions in one instrument. Preferably, the instrument should be made from as few pieces as possible to lower the cost of manufacture and the retail price.